This non-provisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application Nos. 2001-055135 and 2001-162436 filed in Japan on Feb. 28, 2001 and May 30, 2001, respectively, the entirety of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an internal combustion engine in which a piston slidably fitted in a cylinder is connected to a crankshaft via a connecting rod.
2. Description of Background Art
FIGS. 9(A) to 9(C) illustrate a background art four-cycle/single-cylinder internal combustion engine.
An internal combustion engine E includes a cylinder 01, a piston 02 slidably fitted in the cylinder 01, a cylinder head 03 connected to the cylinder 01, a combustion chamber 04 formed at a bottom plane of the cylinder head 03 in such a manner as to face to the cylinder 01, a crankshaft 05, and a connecting rod 06 for connecting the piston 02 to the crankshaft 05. The piston 02 is disposed at a position between the cylinder head 03 and the crankshaft 05.
FIG. 9(A) illustrates a state where the piston 02 is located at a top dead center position. In this state, a crank angle xcex8 is 0xc2x0. FIG. 9(C) illustrates a state where the piston 02 is located at a bottom dead center position. In this state, the crank angle xcex8 is 180xc2x0. FIG. 9(B) illustrates a state where the piston 02 is located at a mid point between the top dead center and the bottom dead center positions. In this state, the crank angle xcex8 is not 90xc2x0, but an angle xcex8a smaller than 90xc2x0. The reason for this the fact that at each of the top dead center and the bottom dead center positions, the connecting rod 06 is located on a cylinder axial line L. However, at the mid point, the connecting rod 06 is inclined by an angle xcfx86 from the cylinder axial line L.
Referring to FIG. 8, a relationship between the crank angle xcex8 from the top dead center position of the internal combustion engine E and a displacement x of the piston 02 from the top dead center position is shown by a chain line. In the figure, a stroke of the piston 02 between the top dead center and the bottom dead center positions is set to 2R (R: crank radius). As described with reference to FIG. 9(B), when the piston 02 is located at the mid point between the top dead center and the bottom dead center positions (at which a displacement x of the piston 02 is R), the crank angle xcex8 becomes the angle xcex8a smaller than 90xc2x0. On the other hand, in a solid sine curve (x=R sin (xcex8xe2x88x9290xc2x0)+R), when the piston 02 is located at the mid point between the top dead center and the bottom center, the crank angle xcex8 becomes 90xc2x0.
In this way, according to the background art internal combustion engine E, it becomes apparent that the line (shown by the chain line) showing the relationship between the crank angle xcex8 and the displacement x of the piston 02 is positioned over the solid sine curve. This means that when the piston 02 is moved down from the top dead center position at the initial stage of an expansion stroke, a ratio of an increased amount of the displacement x of the piston 02 to an increased amount of the crank angle xcex8 is larger than the characteristic shown by the solid sine curve.
By the way, to increase thermal efficiency of the internal combustion engine E, it may be desirable to increase the degree of constant volume of a fuel-air mixture at the time of combustion. This will be more fully described below. When the piston 02 is located in the vicinity of the top dead center position, combustion of a fuel-air mixture starts, and as the piston 02 is moved down, a volume of the combustion chamber 04 over the piston 02 is increased. At this time, as a ratio of an increased amount of the volume of the combustion chamber 04 to an increased amount of the crank angle xcex8 becomes smaller, the above-described degree of constant volume becomes higher, with a result that the thermal efficiency is improved. From this viewpoint, in the background art internal combustion engine E shown in FIGS. 9(A) to 9(C), the ratio of an increased amount of the volume of the combustion chamber 04 to an increased amount of the crank angle xcex8 from the top dead center position becomes larger, so that the degree of constant volume becomes lower. This is inconvenient in terms of increasing the thermal efficiency of the internal combustion engine E.
In view of the foregoing, the present invention has been made, and an object of the present invention is to increase a thermal efficiency of an internal combustion engine by increasing the degree of constant volume of a fuel-air mixture at the time of combustion in the internal combustion engine.
To solve the above object, according to a first aspect of the present invention, there is provided an internal combustion engine in which a piston slidably fitted in a cylinder is connected to a crankshaft via a connecting rod, wherein a cylinder head in which a combustion chamber is defined is disposed between the piston and the crankshaft.
With this configuration, since a cylinder head in which a combustion chamber is defined is disposed between a piston and a crankshaft in an internal combustion engine, as compared with a background art internal combustion engine in which a combustion chamber is disposed opposite to a crankshaft with a piston located therebetween, a ratio of an increased amount of the volume of the combustion chamber to an increased amount of a crank angle of the piston from the top dead center position can be suppressed at a small value. As a result, it is possible to increase the degree of constant volume of a fuel-air mixture at the time of combustion and hence to increase thermal efficiency of the internal combustion engine. Furthermore, since a tensile load is applied to a connecting rod in an expansion stroke, it is not required to take buckling into account as compared with the background art internal combustion engine in which a compressive load is applied to a connecting rod. As a result, it is possible to lower a strength of the connecting rod and hence to reduce the weight thereof.
According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, an intake valve and an exhaust valve are provided in the cylinder head in such a manner as to be open in a V-shape, and a valve mechanism and the crankshaft are disposed between the intake valve and the exhaust valve.
With this configuration, since a valve mechanism and a crankshaft are disposed between an intake valve and an exhaust valve provided in a cylinder head in such a manner as to be opened in a V-shape, it is possible not only to simplify a power transmission route from the crankshaft to the valve mechanism by making the crankshaft and the valve mechanism closer to each other but also to lower the total height of the internal combustion engine.
According to a third aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a pair of connecting rods are disposed on opposite axial end sides of the crankshaft in such a manner as to locate the piston therebetween.
With this configuration, since a pair of connecting rods are disposed on opposite axial end sides of a crankshaft in such a manner as to locate a piston therebetween, it is possible to prevent an unbalanced load from being applied to the piston while avoiding interference of the connecting rods with the piston.
According to a fourth aspect of the present invention, there is provided a reciprocating internal combustion engine in which a stroke volume is not changed during a cycle, wherein values of x, xcex8, and R satisfy an equation of x less than R sin (xcex8xe2x88x9290xc2x0)+R, where x is a displacement of a piston moved toward a bottom dead center position from a top dead center position taken as a reference point, xcex8 is a crank angle from the top dead center position, and R is a crank radius,
With this configuration, a ratio of an increased amount of a volume of a combustion chamber to an increased amount of a crank angle can be suppressed at a small value. This makes it possible to increase the degree of constant volume of a fuel-air mixture at the time of combustion and hence to increase thermal efficiency.
According to fifth aspect of the present invention, in addition to the configuration of the fourth aspect of the present invention, a cylinder head in which a combustion chamber is defined is disposed between a piston and a crankshaft, and a distance between a lower end of a piston ring and an upper end of a piston pin is larger than a stroke of the piston.
With this configuration, since a cylinder head in which a combustion chamber is defined is disposed between a piston and a crankshaft, a tensile load is applied to a connecting rod. Accordingly, it is not required to take buckling into account as compared with the background art internal combustion engine in which a compressive load is applied to a connecting rod. As a result, it is possible to lower a strength of the connecting rod and hence to reduce the weight thereof. Furthermore, since a distance between a lower end of a piston ring and an upper end of a piston pin is set to be larger than a stoke of the piston, the piston ring is not removed from the lower end of the cylinder when the piston reaches the bottom dead center.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.